This invention relates to a twist capsule which conducts signals on a continuous conductor between an input and an output which are rotatable relative to one another around the axis of the twist capsule.
Rotary joints for conducting signals between two points which are rotatable relative to one another are well known in the art. A slip ring is a type of rotary joint which is used when unlimited rotation is required. A slip ring comprises a sliding brush element which rides on the surface of a ring. Sliding contact slip rings are prone to wear due to the surface contact between the brush and the ring and are often a source of electrical noise which degrades the signal.
A twist capsule is another type of rotary joint which can be used if only limited rotation is required. U.S. Pat. No. 3,599,166 issued to Wendell et al shows a twist capsule in which a flat cable is wound in a spiral around the axis of the twist capsule. The inner and outer portions of the capsule are rotatable relative to one another in both clockwise and counterclockwise directions. Such rotation causes a coiling and uncoiling of the spirally wound flat cable around the capsule axis and around itself. Over a period of extended use, the coiling and sliding of the adjacent layers of cable on itself causes an abrasion of the cable insulation which can lead to capsule failure. Additionally, because one end of the flat cable is located in the center of the spiral, individual leads must be attached to that end of the flat cable in order to connect the cable to external wiring. The attachment of the leads to the flat cable is time consuming and adds undesirable cost and complexity to the capsule assembly.
It would be desirable to provide a limited rotation rotary joint which avoids the drawbacks of a spiral wrap device.